1. Field of the Invention
The invention pertains to sonar arrays and more particularly to sonar arrays that form beams steerable in two dimensions.
2. Description of the Prior Art
Two dimensional beam steering in sonar systems requires the insertion of variable time delay elements between hydrophones in each vertical array for vertical plane beam steering and variable time delay elements between the vertical line arrays for horizontal plane beam steering. An approach employed in the prior art utilizes a cable for each hydrophone element, runs each cable through the hull of the ship, and processes all signals, received through these cables, in a beam former to provide the necessary delays for both horizontal and vertical plane steering. Since sonar systems may utilize in the order of 1,000 hydrophone elements, even with groupings of conductors into multi-conductor cables, excessive hull penetrations, numerous front end analog channels, and a beam former of considerable complexity are required. Significant simplification is realized by operating the system at a fixed depression angle, for which fixed time delays are inserted between elements in a vertical column. The signals from the elements in each column are summed to form substantially equal vertical beams. The signals at the column output terminals may then be processed to perform the desired beam steering in the bearing plane. This method accomplishes considerable reduction in system complexity at the sacrifice of sonar beam and system flexibilities.